Long-range force of attraction between solvophobic surfaces in water and organic liquids containing dissolved air

An atomic force microscope has been employed to measure the force of intera ction between a micron-sized colloidal sphere and a flat plate, both coated with a copolymer of perfluoro(2,2-dimethyl-1,3-dioxole) and tetrafluoroeth ylene (Teflon AF1600) in water, glycerol, formamide, ethylene glycol, ethyl ammonium nitrate, formic acid, ethanol, methanol, diiodomethane, 1-bromonap hthalene, hexadecane, and hexane. A long-range force of attraction was meas ured in water and, with the exception of the n-alkanols and n-alkanes, all the organic liquids. The results indicate that there is a macroscopic long- range attraction between solvophobic surfaces that has a different origin f rom that of the hydrophobic interaction observed at the molecular level, Th e results also indicate that there is a "solvophobic force" that is not due to either orientational ordering propagated by hydrogen bonds, electrostat ic (or polarization) effects, or condensates of "loosely attached" surface material; all mechanisms that have been invoked previously to explain the m acroscopic "hydrophobic force". The force curves measured in the organic li quids provide a new perspective which is consistent with the hypothesis tha t submicroscopic air bubbles adhering to the macroscopic surfaces are respo nsible for a long-range attraction.